This document has been reviewed as part of the transport area review team's
ongoing effort to review key IETF documents. These comments were written
primarily for the transport area directors, but are copied to the document's
authors and WG to allow them to address any issues raised and also to the IETF
discussion list for information.

When done at the time of IETF Last Call, the authors should consider this
review as part of the last-call comments they receive. Please always CC
tsv-art@ietf.org if you reply to or forward this review.

The draft updates RFC 6553 to use a different IPv6 hop-by-hop option type for RPL packets, to avoid some issues discovered through deployment experience. This looks to require a flag day cutover, and hence has some potential interoperability concerns, but introduces no transport concern. The draft also describes a number of clarifications around when to use the RPL hop-by-hop option header and when to use IP-in-IP tunnelling, described based on a set of use case examples.

There do not look to be any new transport-related concerns with this draft.

The draft does not mention ECN when using IPv6-in-IPv6 tunneling. It is perhaps implied, but a reference to RFC 6040 would be helpful to clarify how ECN bits are copied between inner and outer headers when encapsulating and decapsulating packets from an IPv6-in-IPv6 tunnel. ECN is seeing increasing use in transport protocols, so correctly propagating this information is important.